Solvent separation method

ABSTRACT

A method for separating solvent-containing water, which is generated in the process for producing an ashless coal, into a solvent and water readily without using any adsorbent or the like (a solvent separation method). The solvent separation method comprises: a solvent-containing water supply step of supplying the solvent-containing water into a pressure vessel for solvent separation purposes; and a temperature retention step of retaining the temperature of the solvent-containing water that has been supplied into the pressure vessel for solvent separation purposes at a predetermined temperature (e.g., 100 to 180 DEG C. inclusive). In the pressure vessel for solvent separation purposes, water in the liquid form moves downward and the solvent moves upward due to the difference between the density of water and the density of the solvent at the predetermined temperature. In this manner, the solvent-containing water can be separated into the solvent and water.

TECHNICAL FIELD

The present invention relates to a method for separatingsolvent-containing water, which is generated in the process forproducing an ashless coal by removing ash from a coal, into a solventand water.

BACKGROUND ART

Examples of methods for producing an ashless coal include a methoddescribed in PTL 1. PTL 1 describes a method for producing an ashlesscoal, wherein a slurry is prepared by mixing a coal and a solvent, asolvent-soluble coal component is extracted by heating the resultingslurry, a solution containing the solvent-soluble coal component isseparated from the slurry, from which the coal component has beenextracted, and thereafter, an ashless coal is obtained by recovering thesolvent from the separated solution. An oil component derived from acoal is used as the solvent.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No 2005-120185

SUMMARY OF INVENTION Technical Problem

Here, in the above-described process for producing an ashless coal,water (H₂O) is produced from the coal serving as a raw material. In theextraction of the coal component, the slurry is heated to a temperatureof, for example, 300 to 420 DEG C. The coal undergoes a thermaldecomposition reaction under such high temperatures, and methane (CH₄),carbon dioxide (CO₂), water (H₂O), and the like are produced. Also, thecoal serving as a raw material contains water in the first place, andthe water is separated from the coal in extraction of the coal componentwith the solvent.

The water (H₂O) produced from the coal through thermal decomposition andthe water (H₂O) separated from the coal in extraction of the coalcomponent are discharged as a gas (water vapor) to the outside of thesystem of an ashless coal producing facility, while much solvent ispresent in the gas (solvent-containing water). Therefore, if the gasconcerned is entirely discarded, a solvent loss increases significantly,and fresh supplementation of much solvent becomes necessary. As aresult, the running cost increases.

Meanwhile, in order to discard the gas containing the solvent, forexample, a treatment to remove the solvent from the gas by using anadsorbent is necessary, and in the case where the amount of solventcontained in the gas is large, the treatment cost increasessignificantly. Also the solvent adsorbed by the adsorbent is not readilyseparated from the solvent. That is, reuse of an adsorbent which hasbeen used for the adsorption treatment is difficult.

The present invention has been made in consideration of theabove-described circumstances, and it is an object to provide a methodcapable of separating solvent-containing water, which is generated inthe process for producing an ashless coal, into a solvent and waterreadily without using any adsorbent or the like.

Solution to Problem

The present invention is a solvent separation method for separatingsolvent-containing water, which is generated in the process forproducing an ashless coal, into a solvent and water, the methodincluding an extraction step of extracting a solvent-soluble coalcomponent by heating a slurry obtained by mixing a coal and the solvent,a separation step of separating a solution containing thesolvent-soluble coal component from the slurry obtained in theabove-described extraction step, and an ashless coal acquisition step ofobtaining an ashless coal by vaporizing and separating the solvent fromthe solution separated in the above-described separation step. Thissolvent separation method is characterized in that a solvent-containingwater supply step of supplying the above-described solvent-containingwater into a pressure vessel for solvent separation purposes and atemperature retention step of retaining the temperature of theabove-described solvent-containing water that has been supplied into theabove-described pressure vessel for solvent separation purposes at apredetermined temperature are included and the above-describedsolvent-containing water is separated into the solvent and water bymoving water in the liquid form downward and moving the solvent upwardin the above-described pressure vessel for solvent separation purposesdue to the difference between the density of water and the density ofthe solvent at the predetermined temperature.

In this regard, the term “solvent-containing water” refers to water inthe state in which a solvent and water are mixed (mixed state)regardless of a liquid state or a gas state. Also, the term “isgenerated in the process for producing an ashless coal” is in the senseof being generated as a by-product in any portion of the process forproducing an ashless coal.

Advantageous Effects of Invention

According to the present invention, the solvent-containing water, whichis generated in the process for producing an ashless coal, can beseparated into the solvent and water readily without using any adsorbentor the like. As a result, the adsorbent can be reused, the solvent losscan he reduced and, in addition, the water disposal cost can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an ashless coal producing facilityprovided with a pressure vessel for solvent separation purposes toseparate a solvent containing water into a solvent and water.

FIG. 2 is a diagram illustrating the outline of a separation test toseparate a solvent-containing water into a solvent and water.

FIG. 3 is a graph showing the results of the separation test.

DESCRIPTION OF EMBODIMENTS

The embodiments according to the present invention will be describedbelow with reference to drawings.

As shown in FIG. 1, an ashless coal producing facility 100 is providedwith a coal hopper 1, a solvent tank 2, a slurry preparation vessel 3, atransfer pump 4, a preheater 5, an extraction vessel 6, a gravitysettling vessel 7, a filter unit 8, and a solvent separator 9sequentially from the upstream side of an ashless coal (HPC) productionprocess. The solvent separator 9 vaporizes and separates a solvent froma solution (supernatant liquid) separated in the gravity settling vessel7.

Also, on the downstream side of the gravity settling vessel 7, a solventseparator 10 to vaporize and separate the solvent from asolvent-insoluble component concentrate (solid content concentrate)separated in the gravity settling vessel 7 (to separate and recover thesolvent from the solid content concentrate) is disposed.

Also, the ashless coal producing facility 100 is provided with apressure vessel for solvent separation purposes 11 to separate thesolvent-containing water into the solvent and water. This pressurevessel for solvent separation purposes 11 is connected to the extractionvessel 6 with a pipe 25. That is, in the present embodiment, thesolvent-containing water in the gas, which is generated in theextraction step in the process for producing an ashless coal, issupplied from the extraction vessel 6 to the pressure vessel for solventseparation purposes 11, so as to be separated into the solvent in theliquid form and water in the liquid form.

In this regard, the pressure vessel for solvent separation purposes 11may be connected to the gravity settling vessel 7 rather than theextraction vessel 6 with a pipe or the like. That is, thesolvent-containing water (the solvent is a liquid and the solvent ismixed into the water vapor) in the gas, which is generated in theextraction step, may be supplied from the gravity settling vessel 7 tothe pressure vessel for solvent separation purposes 11, so as to beseparated into the solvent and water. Meanwhile, in the case where avery small amount of water is generated in the gravity settling vessel7, the solvent-containing water generated here can be separated into thesolvent and water in the pressure vessel for solvent separation purposes11 by connecting the pressure vessel for solvent separation purposes 11to the gravity settling vessel 7.

Furthermore, one pressure vessel for solvent separation purposes 11 maybe connected to both the extraction vessel 6 and the gravity settlingvessel 7, or each of the extraction vessel 6 and the gravity settlingvessel 7 may be connected to one pressure vessel for solvent separationpurposes 11. In the case where water remains in the slurry supplied tothe gravity settling vessel 7, the water can be removed by dischargingthe solvent-containing water in the gas containing the solvent from thegravity settling vessel 7 to the pressure vessel for solvent separationpurposes 11.

Also, the pressure vessel for solvent separation purposes 11 may beconnected to the slurry preparation vessel 3 with a pipe or the like.This is because in the case where a coal containing much water ishandled, the slurry preparation vessel 3 is heated to 100 to 120 DEG C.,which is in the vicinity of the boiling point of water, to recover waterfrom the coal through vaporization and, thereby, the water concentrationin the slurry transferred to the extraction step can be decreased. Thesolvent-containing water generated here can be supplied from the slurrypreparation vessel 3 to the pressure vessel for solvent separationpurposes 11, so as to be separated into the solvent and water.

Also, a tank may be disposed at some midpoint of the pipe 25 connectedto the pressure vessel for solvent separation purposes 11. Thesolvent-containing water is condensed once into a liquid in the tankconcerned (the solvent-containing water is condensed by lowering thetemperature of the solvent-containing water) and, thereafter, water isvaporized from the solvent-containing water by heating to a temperaturehigher than or equal to the boiling point of water again. Thus a vapor(including the solvent) resulting from concentration of the water istransferred from the tank concerned to the pressure vessel for solventseparation purposes 11. According to this step, the solventconcentration in the solvent-containing water transferred to thepressure vessel for solvent separation purposes 11 is reduced, and thesolvent loss factor can be further reduced. In this regard, the solventremaining in the tank is drawn from the tank and is reused.

Here, an ashless coal production method (process for producing anashless coal) includes an extraction step, a separation step, and anashless coal acquisition step. Each of these steps will be describedbelow and, in addition, a method for separating the solvent-containingwater, which is generated in the process for producing an ashless coal,into the solvent and water will be described. In this regard, the coalserving as a raw material in the production of the ashless coal is notspecifically limited. A bituminous coal having a high extraction rate(ashless coal recovery percentage) may be used or a cheaper bony coal(sub-bituminous coal, brown coal) may be used. Meanwhile, the ashlesscoal refers to a coal having an ash content of 5 percent by weight orless, and preferably 3 percent by weight or less.

(Extraction Step)

The extraction step is a step of extracting a solvent-soluble coalcomponent through heating of the slurry obtained by mixing the coal andthe solvent, in the present embodiment, this extraction step is dividedinto the slurry preparation step of preparing the slurry by mixing thecoal and water and the solvent-soluble component extraction step ofextracting (dissolving into the solvent) a solvent-soluble coalcomponent by heating the slurry prepared in the slurry preparation step.

In extraction of the solvent-soluble coal component through heating ofthe slurry obtained by mixing the coal and the solvent, a solvent havinga large solvent power with respect to a coal, which is an aromaticsolvent (hydrogen donor solvent or solvent not having a hydrogendonating property) in many cases, and a coal are mixed and are heated,so that organic components in the coal are extracted.

The solvent not having a hydrogen donating property is a coal derivativewhich is refined mainly from a coal carbonization product and which is asolvent primarily containing a bicyclic aromatic. This solvent nothaving a hydrogen donating property is stable even in a heated state,has excellent affinity for a coal, where the proportion of a solublecomponent (here, a coal component) extracted by a solvent (may bereferred to as an extraction rate) is high, and is a solvent readilyrecoverable by a method of distillation or the like. Examples of primarycomponents of the solvents not having a hydrogen donating propertyinclude naphthalene, methylnaphthalene, dimethylnaphthalene, andtrimethylnaphthalene, which are bicyclic aromatics. Components of othersolvents not having a hydrogen donating property include naphthalenes,anthracenes, fluorenes, which have aliphatic side chains, and inaddition, biphenyls and alkylbenzenes having long aliphatic side chainsare also included in the solvent not having a hydrogen donatingproperty.

In this regard, in the case explained above, the solvent not having ahydrogen donating property is used as the solvent. However, as a matterof course, hydrogen donating compounds (including coal liquefaction oil)typified by tetralin may be used as the solvent. In the case where thehydrogen donor solvent is used, the yield of ashless coal is improved.

The specific gravities of these solvents (ratio to the weight of waterhaving the same volume) is about 1 at room temperature (ambienttemperature).

Meanwhile, the boiling point of the solvent is not specifically limited.Solvents having boiling points of, for example, 180 to 300 DEG C., inparticular 240 to 280 DEG C. are used preferably from the view point of,for example, reduction in pressures in the extraction step and theseparation step, the extraction rate in the extraction step, the solventrecovery percentages in the ashless coal acquisition step and the like.

<Slurry Preparation Step>

The slurry preparation step is executed in the slurry preparation vessel3 shown in FIG. 1. The coal serving as a raw material is put into theslurry preparation vessel 3 from the coal hopper 1 and, in addition, thesolvent is put into the slurry preparation vessel 3 from the solventtank 2. The coal and the solvent put into the slurry preparation vessel3 are mixed with an agitator 3 a to become a slurry composed ref thecoal and the solvent.

The mixing ratio of the coal to the solvent is, for example, 10 to 50percent by weight in terms of dry coal, and more preferably 20 to 35percent by weight.

<Solvent-Soluble Component Extraction Step>

The solvent-soluble component extraction step is executed in thepreheater 5 and the extraction vessel 6 shown in FIG. 1. The slurryprepared in the slurry preparation vessel 3 is once supplied to thepreheater 5 by the transfer pump 4, so as to be heated to thepredetermined temperature and, thereafter, is supplied to the extractionvessel 6, where extraction is performed while agitation with theagitator 6 a and retention at the predetermined temperature areperformed.

The heating temperature in the solvent-soluble component extractionstep, is not specifically limited in so far as the solvent-solublecomponent is dissolved and is, for example, 300 to 420 DEG C., and morepreferably 360 to 400 DEG C. from the view points of sufficientdissolution of the solvent-soluble component and an improvement inextraction rate.

Also, the heating time (extraction time) is not specifically limited butis, for example, 10 to 60 minutes from the view points of sufficientdissolution and an improvement in extraction rate. The heating time is atotal of the heating times in the preheater 5 and the extraction vessel6 shown in FIG. 1.

In this regard, the solvent-soluble component extraction step isperformed in the presence of an inert gas, e.g, nitrogen. The pressurein the extraction vessel 6 is preferably 1.0 to 2.0 MPa, althoughdepending on the temperature in the extraction and the vapor pressure ofthe solvent used. In the case where the pressure in the extractionvessel 6 is lower than the vapor pressure of the solvent, the solvent isvolatilized and is not confined in the liquid phase, so that extractioncannot be performed. In order to confine the solvent in the liquidphase, a pressure higher than the vapor pressure of the solvent isnecessary. On the other hand, if the pressure is too high, the apparatuscost and the operation cost increase, so that there is no economy.

(Method for Separating Solvent and Water)

As described above, in extraction of the coal component, the slurry isheated to a temperature of, for example, 300 to 420 DEG C. Here, undersuch high temperatures, the coal undergoes a thermal decompositionreaction, and methane (CH₄), carbon dioxide (CO₂), water (H₂O), and thelike are produced. Also, the coal serving as a raw material containswater in the first place, and water is insoluble in the solvent, so thatwater is separated from the coal in extraction of the coal componentwith the solvent.

(Solvent-Containing Water Supply Step)

The solvent-containing water supply step is a step of supplying thesolvent-containing water to the pressure vessel for solvent separationpurposes. The water (H₂O) produced from the coal through thermaldecomposition and the water (H₂O) separated from the coal in extractionof the coal component are in the state of a gas containing the solvent(the state of solvent-containing water vapor) and is supplied(discharged) to the pressure vessel for solvent separation purposes 11through the pipe 25. The temperature in the pressure vessel for solventseparation purposes 11 is specified to be lower than the temperature inthe extraction vessel 6 and, therefore, the water vapor is condensedinto a liquid.

(Temperature Retention Step)

The temperature retention step is a step of retaining the temperature ofthe solvent-containing water that has been supplied into the pressurevessel for solvent separation purposes 11 at a predetermined temperatureand is executed in the pressure vessel for solvent separation purposes11 shown in FIG. 1. The solvent-containing water supplied to thepressure vessel for solvent separation purposes 11 from the extractionvessel 6 is heated in the pressure vessel for solvent separationpurposes 11 with a heater 11 a in such a way that the temperaturebecomes constant at a temperature at which the difference between thedensity of the water and the density of the solvent is large. Forexample, the temperature is retained at 100 to 180 DEG C. inclusive (apredetermined temperature within the range of 100 to 180 DEG C.).Consequently, the solvent and water are separated by moving of the waterin the liquid form downward to the lower portion of the pressure vesselfor solvent separation purposes 11 and moving of the solvent upward tothe upper portion of the pressure vessel for solvent separation purposes11 due to the difference between the density of the water and thedensity of the solvent at the temperature concerned. In order to improvethe separability between the solvent and the water, it is preferablethat the solvent-containing water be allowed to stand for thepredetermined time. Also, it is preferable that the pressure vessel forsolvent separation purposes 11 be heat-insulated by a heat insulatingmaterial to retain the temperature of the solvent-containing water at atemperature higher than or equal to the predetermined temperature. Inthis regard, the term “stand” refers to remain stationary withoutagitation and the like.

The solvent collected in the upper portion of the pressure vessel forsolvent separation purposes 11 is drawn from the upper portion of thepressure vessel for solvent separation purposes 11, and the watercollected in the lower portion of the pressure vessel for solventseparation purposes 11 is drawn from the lower portion of the pressurevessel for solvent separation purposes 11. The drawn solvent is returnedto the solvent tank 2 and is reused. The drawn water is discarded.

Also, the temperature retention step is performed preferably in thepresence of an inert gas, e.g., nitrogen. That is, it is preferable thatthe inert gas, e.g., nitrogen, be filled in the pressure vessel forsolvent separation purposes 11. The pressure in the pressure vessel forsolvent separation purposes 11 is specified to be a pressure higher thanthe saturated vapor pressure of water in such a way that a water vaporis condensed and the resulting water keeps the liquid state and isadjusted to be a pressure of, for example, 0.3 to 2.0 MPa byintroduction of a nitrogen gas into the pressure vessel.

Also, the solvent-containing water supplied to the pressure vessel forsolvent separation purposes 11 may be agitated with an agitator or thelike and, thereafter, the agitation may be stopped at the point in timewhen the temperature becomes constant at the predetermined temperature,followed by standing.

Meanwhile, the slurry is heated to a temperature of, for example, 300 to420 DEG C. in the extraction vessel 6. The heater 11 a is not necessaryinsofar as the temperature of the solvent-containing water supplied fromthe extraction vessel 6 to the pressure vessel for solvent separationpurposes 11 can be retained at a temperature of, for example, 120 DEG C.or higher for a predetermined time without heating.

(Case Where Extraction Vessel 6 is not Provided)

In some cases, the extraction vessel 6 is not provided, and asolvent-soluble coal component is extracted in the pipe between thepreheater 5 and the gravity settling vessel 7. For example, the lengthof the pipe between the preheater 5 and the gravity settling vessel 7 isspecified to be sufficient for extraction of the coal component and thecoal component is extracted in the pipe between the preheater 5 and thegravity settling vessel 7. The coal is directly supplied into the pipe,through which the solvent heated to a high temperature (for example, 380DEG C.) is passed, between the preheater 5 and tbe gravity settlingvessel 7. In this case, the pressure vessel for solvent separationpurposes 11 is connected to the gravity settling vessel 7, thesolvent-containing water is supplied (discharged) from the gravitysettling vessel 7 to the pressure vessel for solvent separation purposes11, and the solvent-containing water is separated into the solvent andwater.

The explanation of the production process of an ashless coal will becontinued.

(Separation Step)

The separation step is a step of separating a solution containing thecoal component dissolved in the solvent from the slurry obtained in theextraction step. Put another way, the separation step is a step ofseparating the slurry obtained in the extraction step into the solutioncontaining the coal component dissolved in the solvent and asolvent-insoluble component concentrate (solid content concentrate).This separation step is executed in the gravity settling vessel 7 shownin FIG. 1. The slurry obtained in the extraction step is separated intoa supernatant liquid as a solution and a solid content concentrate dueto gravity in the gravity settling vessel 7 (gravity settling method).The supernatant liquid in the upper portion of the gravity settlingvessel 7 discharged into the solvent separator 9 through the filter unit8, as necessary, and in addition, the solid content concentrate settledinto the lower portion of the gravity settling vessel 7 is dischargedinto the solvent separator 10.

The gravity settling method is a method for settling and separating thesolvent-insoluble component through the use of the gravity by holdingthe slurry in the vessel. A continuous separation treatment is possibleby supplying the slurry into the vessel continuously while thesupernatant liquid is discharged from the upper portion and the solidcontent concentrate is discharged from the lower portion continuously.

In order to prevent reprecipitation of the solvent-soluble componenteluted from the coal, it is preferable that the inside of the gravitysettling vessel 7 be heat-insulated or heated and pressurized. Theheating temperature is, for example, 300 to 380 DEG C., and the pressurein the vessel is specified to be, for example, 1.0 to 3.0 MPa.

Meanwhile, as for the method for separating the solution containing thecoal component dissolved in the solvent from the slurry obtained in theextraction step, a filtration method, a centrifugal separation method,and the like are mentioned besides the gravity settling method.

(Ashless Coal Acquisition Step)

The ashless coal acquisition step is a step of obtaining an ashless coalby vaporizing and separating the solvent from the solution (supernatantliquid) separated in the above-described separation step. This ashlesscoal acquisition step is executed in the solvent separator 9 shown inFIG. 1.

As for the method for separating the solvent from the solution(supernatant liquid), a common distillation method or vaporizationmethod can be used and, for example, a flash distillation method isused. A separated and recovered solvent can be used repeatedly bycirculation to the slurry preparation vessel 3. An ashless coal (HPC)containing substantially no ash (for example, ash content is 3 percentby weight or less) can be obtained from the supernatant liquid byseparation and recovery of the solvent. The ashless coal hardly containsash, contains no water, and exhibits a calorific value higher than thatof the raw material coal. Furthermore, the plastic property of coal,which is particularly important quality of a raw material for the cokefor steelmaking, is improved to a great extent, and even when the rawmaterial coal does not have the plastic property of coal, the resultingashless coal (HPC) has good plastic property of coal. Therefore, theashless coal can be used as, for example, a blend coal of the rawmaterial for coke.

(By-Product Coal Acquisition Step)

A by-product coal acquisition step is a step of obtaining a by-productcoal by vaporizing and separating the solvent from the solvent-insolublecomponent concentrate (solid content concentrate) separated in thegravity settling vessel 7. This by-product coal acquisition step is astep of recovering the solvent from the solid content concentratethrough vaporization and separation and is executed in the solventseparator 10 shown in FIG. 1. In this regard, the by-product coalacquisition step is not always a necessary step.

As for the method for separating the solvent from the solid contentconcentrate, a common distillation method or vaporization method can beused as with the above-described ashless coal acquisition step. Aseparated and recovered solvent can be used repeatedly by circulation tothe slurry preparation vessel 3. A by-product coal (may be referred toas RC, or residual coal), in which the solvent-insoluble componentcontaining ash and the like has been concentrated, can be obtained fromthe solid content concentrate by separation and recovery of the solvent.The by-product coal contains ash but no water and has a sufficientcalorific value. The by-product coal does not exhibit the plasticproperty of coal. However, an oxygen-containing functional group hasbeen eliminated, so that in the case of use as a blend coal, the plasticproperty of coal of the other coal contained in this blend coal is nothindered. Therefore, this by-product coal can be used as part of blendcoal of the raw material for coke as with a common non- orslightly-caking coal or can be used as various fuels rather than the rawmaterial for coke. In this regard, the by-product coal may be discardedwithout being recovered.

EXAMPLES

Experiments to separate a solvent-containing water into a solvent andwater were performed. FIG. 2 is a diagram illustrating the outline of aseparation test to separate the solvent-containing water into thesolvent and water. An oil component (coal derivative) refined from acoal containing methylnaphthalene, which was a bicyclic aromatic, as aprimary component was used as the solvent. Distilled water was used asthe water.

A vertically long autoclave 50 used in the experiment was a cylindricalpressure vessel having a diameter of 62.3 mm and had a structure inwhich a liquid was drawn from the bottom of the autoclave 50 and aplurality of places at the predetermined heights from the bottom, asshown in FIG. 2. The liquid was sampled from six places in total at theheights of 0 mm, 170 mm, 380 mm, 590 mm, 700 mm, and 800 mm, where theheight of the bottom of the autoclave 50 was specified to be 0 mm. Inthis regard, an agitator 50 a was disposed in the inside of theautoclave 50. A nitrogen gas was filled in the autoclave 50, and thepressure in the autoclave 50 was adjusted to 1.5 MPa.

A solvent: 1,200 g and water: 1,200 g were put into the autoclave 50. Atroom temperature (ambient temperature), the solvent and the water werein a mixed state and the separability was very poor. That is, at roomtemperature (ambient temperature), there was almost no differencebetween the density of the water and the density of the solvent.

The temperature of the mixed solution composed of the solvent and thewater was raised to the predetermined temperature while agitation wasperformed. The temperature conditions were specified to be 50 DEG C., 90DEG C., 100 DEG C., 120 DEG C., 150 DEG C., and 200 DEG C. The agitationwas stopped when the temperature of the mixed solution became constantat a predetermined temperature. After the agitation was stopped,standing was performed for 30 minutes. Subsequently, the liquid wastaken out of the autoclave 50 into sampling containers 51 a to 51 f, andthe water concentration of the liquid was measured. The results areshown in Table 1. FIG. 3 is a graph showing the results shown in Table1, the vertical axis indicates the height from the bottom of theautoclave 50, and the horizontal axis indicates the water concentration.

TABLE 1 Water concentration after standing for 30 minutes [wt %]Sampling container No. (height from bottom) 50° C. 90° C. 100° C. 120°C. 150° C. 200° C. 51a — — — — 0.63 2.16 (800 mm) 51f 40.1 2.69 0.812.18 1.94 6.5 (700 mm) 51b 11.7 48.0 0.27 2.81 0.84 29.2 (590 mm) 51c41.0 70.9 70.2 95.4 72.3 37.3 (380 mm) 51d 54.4 65.1 89.7 91.2 97.6 —(170 mm) 51e 12.5 33.3 93.0 94.6 98.0 68.8 (0 mm)

As is clear from Table 1 and FIG. 3, in the case where the retentiontemperature was 50 DEG C., the water concentration fluctuated as theheight in the autoclave 50 was changed, and obvious tendency of thesolvent and the water to separate was not observed visually. In thecases of 90 DEG C. and 200 DEG C., low values of water concentrationwere shown in the upper portion of the autoclave 50, but the values ofwater concentration at the bottom were not sufficiently high (thesolvent was included), so that the separation performance was low.

On the other hand, in the cases where the retention temperatures were100 DEG C., 120 DEG C., and 150 DEG C., low values of waterconcentration were shown in the upper portion of the autoclave 50, highvalues were shown in the bottom, and large changes were observed withinthe range of 400 mm to 600 mm from the bottom. Consequently, it is clearthat the separation performance of the solvent was high in the cases of100 DEG C., 120 DEG C., and 150 DEG C. In particular, the highest waterconcentration at the bottom of 98 percent by weight was shown in thecase of 150 DEG C. Therefore, it was found that the temperature range inwhich the retention temperature was 150 DEG C. was the best temperaturerange for the solvent separation condition.

On the basis of this separation test, it was made clear that thedifference between the density of the water and the density of thesolvent changed with the temperature to a great extent (depended on thetemperature to a great extent). The present invention has takenadvantage of this property found here.

(Operations and Advantages)

The solvent separation method according to the present inventionincludes the temperature retention step of retaining the temperature ofthe solvent-containing water that has been supplied into the pressurevessel for solvent separation purposes at the predetermined temperature,and the solvent-containing water is separated into the solvent and waterby moving the water in the liquid form downward and moving the solventupward in the above-described pressure vessel for solvent separationpurposes through the use of the difference between the density of thewater and the density of the solvent at the predetermined temperature.In this regard, the pressure vessel is used in order to confine thewater in the liquid phase in the container. According to the presentinvention, the solvent-containing water can be separated into thesolvent and the water readily by retaining the temperature of thesolvent-containing water at the predetermined temperature in thepressure vessel without using an adsorbent or the like. Consequently,the adsorbent can be recovered and reused for extracting the coalcomponent, so that the solvent loss can be reduced and, in addition, thewater disposal cost can be reduced. In this regard, thesolvent-containing water supply step of supplying the solvent-containingwater into the pressure vessel for solvent separation purposes may beperformed continuously or be performed discontinuously.

Also, in the above-described temperature retention step, the separationperformance between the solvent and the water can be improved byretaining the temperature of the solvent-containing water at thepredetermined temperature and, in addition, allowing thesolvent-containing water to stand.

Also, in the temperature retention step, the temperature of thesolvent-containing water in the pressure vessel for solvent separationpurposes is retained at a temperature of 100 to 180 DEG C. inclusiveand, thereby, the separation performance between the solvent and thewater becomes very good, so that the separation time can be decreased.There is a merit that the capacity of the pressure vessel for solventseparation purposes can be reduced. More preferably, the temperature ofthe solvent-containing water in the pressure vessel for solventseparation purposes is retained at a temperature of 120 to 150 DEG C.inclusive.

Also, the pressure in the pressure vessel for solvent separationpurposes is specified to be a pressure higher than the saturated vaporpressure of water and, thereby, the water can be completely confined inthe liquid phase in the pressure vessel, so that the separationperformance between the solvent and the water is further improved.

Also, an inert gas is filled in the pressure vessel for solventseparation purposes and, thereby, explosion of the solvent can beprevented.

Also, it is preferable that the solvent-containing water, which isgenerated in the above-described extraction step in the process forproducing an ashless coal, be supplied to the pressure vessel forsolvent separation purposes. Water is generated at the maximum in theextraction step in the process for producing an ashless coal, and a lossof solvent mixed into water and discharged to the outside of the systemcan be reliably reduced by supplying the solvent-containing watergenerated in at least this extraction step to the pressure vessel forsolvent separation purposes and separating the solvent-containing waterinto the solvent and water.

Up to this point, the embodiments according to the present inventionhave been explained. However, the present invention is not limited tothe above-described embodiments and can be variously modified and beexecuted within the scope of the claims.

REFERENCE SIGNS LIST

1: coal hopper

2: solvent tank

3: slurry preparation vessel

4: transfer pump

5: preheater

6: extraction vessel

7: gravity settling vessel

8: filter unit

9, 10: solvent separator

11: pressure vessel for solvent separation purposes

100: ashless coal producing facility

1. A solvent separation method for separating solvent-containing water,which is generated in the process for producing an ashless coal, into asolvent and water, the method comprising: an extraction step ofextracting a solvent-soluble coal component by heating a slurry obtainedby mixing a coal and the solvent; a separation step of separating asolution containing the solvent-soluble coal component from the slurryobtained in the extraction step; and an ashless coal acquisition step ofobtaining an ashless coal by vaporizing and separating the solvent fromthe solution separated in the separation step, wherein asolvent-containing water supply step of supplying the solvent-containingwater into a pressure vessel for solvent separation purposes and atemperature retention step of retaining the temperature of thesolvent-containing water that has been supplied into the pressure vesselfor solvent separation purposes at a predetermined temperature areincluded; and the solvent-containing water is separated into the solventand water by moving water in the liquid form downward and moving thesolvent upward in the pressure vessel for solvent separation purposesdue to the difference between the density of water and the density ofthe solvent at the predetermined temperature.
 2. The solvent separationmethod according to claim 1, wherein in the temperature retention step,the temperature of the solvent-containing water is retained at thepredetermined temperature and the solvent-containing water is allowed tostand.
 3. The solvent separation method according to claim 1, wherein inthe temperature retention step, the temperature of thesolvent-containing water in the pressure vessel for solvent separationpurposes is retained at a temperature of 100 to 180 DEG C. inclusive. 4.The solvent separation method according to claim 1, wherein the pressurein the pressure vessel for solvent separation purposes is specified tobe a pressure higher than the saturated vapor pressure of water.
 5. Thesolvent separation method according to claim 1, wherein an inert gas isfilled in the pressure vessel for solvent separation purposes.
 6. Thesolvent separation method according to claim 1, wherein thesolvent-containing water, which is generated in the extraction step inthe process for producing an ashless coal, is supplied to the pressurevessel for solvent separation purposes.
 7. The solvent separation methodaccording to claim 2, wherein in the temperature retention step, thetemperature of the solvent-containing water in the pressure vessel forsolvent separation purposes is retained at a temperature of 100 to 180DEG C. inclusive.
 8. The solvent separation method according to claim 2,wherein the pressure in the pressure vessel for solvent separationpurposes is specified to be a pressure higher than the saturated vaporpressure of water.
 9. The solvent separation method according to claim2, wherein an inert gas is filled in the pressure vessel for solventseparation purposes.
 10. The solvent separation method according toclaim 2, wherein the solvent-containing water, which is generated in theextraction step in the process for producing an ashless coal, issupplied to the pressure vessel for solvent separation purposes.